In conventional liquid crystal display devices, a predetermined image can be recognized by utilizing light emitted from a light source provided inside the device (internal light source).
However, with the popularization of mobile telephones, on-board televisions for vehicles, and the like in recent years, there are increasing opportunities of viewing liquid crystal display screens outdoors, and along therewith, there is also a problem that the light intensity from an internal light source is lower than that of outdoor light, and a predetermined screen is made not easily visible.
Furthermore, in mobile applications such as mobile telephones, since the electric power consumption by an internal light source of a liquid crystal display device occupies a large proportion of the total electric power consumption, when the internal light source is used heavily, there is a problem that the duration time of the battery is shortened.
Thus, in order to address these problems, reflective liquid crystal display devices that utilize external light as a light source have been developed.
With such a reflective liquid crystal display device, since external light is utilized as a light source, images can be recognized more clearly when the external light is more intense, and the electric power consumption of an internal light source can also be effectively suppressed.
That is, in regard to such a reflective liquid crystal display device, it has been suggested to incorporate a light diffusion film intended for efficient light diffusion so that external light can be efficiently transmitted to be introduced into the interior of a liquid crystal display device, and the external light can be effectively utilized as a light source (for example, Patent Document 1).
To explain more specifically, Patent Document 1 discloses a liquid crystal device (1112) which includes, as illustrated in FIG. 24(a) to FIG. 24(b), a liquid crystal cell including an upper substrate 1103, a lower substrate 1107, and a liquid crystal layer 1105 interposed therebetween; a light reflecting plate 1110 provided on the side of the lower substrate 1107; and a light control plate (light diffusion film) 1108 provided between the liquid crystal layer 1105 and the light reflecting plate 1110.
Further, a light control plate 1108 for selectively scattering light that is incident at a predetermined angle and also for transmitting light that is incident at angles other than the predetermined light, is provided, and such a light control plate 1108 is disposed in the liquid crystal cell such that the scattering axis direction 1121, which corresponds to the direction of selectively scattering the light incident at a predetermined angle, being projected on the surface of the light control plate 1108, is arranged to be in the direction of almost six o'clock in the liquid crystal cell plane.
Furthermore, regarding the light diffusion film that is used in a reflective liquid crystal display device, various forms are known. However, particularly, a light diffusion film having, within the film, a louver structure that can control the light direction or regulate light dispersibility by having long and thin plate-shaped high refractive index regions and long and thin plate-shaped low refractive index regions arranged alternately in parallel along any one direction along the film plane, is widely used (for example, Patent Documents 2 to 4).
That is, Patent Document 2 discloses a light control film (light diffusion film) which is obtained by irradiating a film-like composition containing plural kinds of compounds having polymerizable carbon-carbon double bonds, with ultraviolet radiation from a particular direction, and curing the composition, and is capable of selectively scattering only light incident at an angle in a particular range, characterized in that at least one compound included in the composition is a compound having plural aromatic rings and one polymerizable carbon-carbon double bond in the molecule.
Furthermore, Patent Document 3 discloses a photocurable composition characterized by containing (A) a fluorene-based compound having a polymerizable carbon-carbon double bond in the molecule; (B) a cation polymerizable compound having a refractive index that is different from that of the fluorene-based compound (A); and (C) a photocation polymerization initiator, and a light control film formed by curing the photocurable composition.
Furthermore, Patent Document 4 discloses a composition for light diffusion film including at least (A) a bisphenol A type epoxy resin or brominated bisphenol A type epoxy resin represented by Formula (5); (B) a radical-polymerizable compound having at least one or more ethylenically unsaturated bonds in the structural unit; (D) a photopolymerization initiator generating a radical species by chemical radiation; and (E) a thermal polymerization initiator generating a cation species by heat, and a light diffusion film produced using the composition. More specifically, a composition for light diffusion film characterized in that at normal temperature, the refractive index of the (B) radical polymerizable compound is lower than the refractive indices of the (A) bisphenol A type epoxy resin or brominated bisphenol A type epoxy resin, and the (C) compound having at least one cationic polymerizable group in the molecule, and a light diffusion film produced using the composition.
wherein in Formula (5), R represents a hydrogen atom or a bromine atom; and the number of repetitions p represents a natural number.
Furthermore, there has been disclosed a method of laminating light diffusion films so that the width of the light diffusion incident angle region can be further expanded (for example Patent Document 5).
That is, Patent Document 5 discloses a screen for projection characterized by being formed by laminating plural sheets of light control films (light diffusion films), in each of which the fog value is angle-dependent, and when light enters at an angle of 0° to 180° with respect to the surface, the light scattering angle range that exhibits a fog value of 60% or higher is 30° or more.
Furthermore, as another method of expanding the width of the light diffusion incident angle region, there has also been disclosed a method of further applying a composition for light diffusion film on a light diffusion film that has been prepared in advance, and then photocuring the composition so as to form two louver structures in the film (for example, Patent Document 6).
That is, Patent Document 6 discloses a method for producing a light control plate (light diffusion film), the method including a first step of retaining on a film a resin composition composed of plural compounds, each having one or more polymerizable carbon-carbon double bonds in the molecule and having a refractive index that is different from the refractive indices of the other compounds, irradiating the composition with ultraviolet radiation from a particular direction, and thereby curing the resin composition; and a second step of retaining (applying) the resin composition on the film of the cured product thus obtained, irradiating the resin composition with ultraviolet radiation from a direction different from that of the first step, and thereby curing the resin composition, characterized in that the second step is repeated as necessary.
Furthermore, as still another method for expanding the width of the light diffusion incident angle region, there has also been disclosed a method of forming a louver structure which is bent to a predetermined extent in a film, by irradiating ultraviolet radiation having a particular wavelength distribution to a composition for light diffusion film (for example, Patent Document 7).
That is, Patent Document 7 discloses a method for producing a light control film (light diffusion film), the method including irradiating a film-like composition containing at least two compounds, each having a polymerizable carbon-carbon bond in the molecule and having a refractive index that is different from the refractive indices of the other compounds, with ultraviolet radiation through an interference filter having a transmittance of 0% to 60% at a wavelength of 313 nm, and thereby curing the composition.
In addition, although it is not a method intended to expand the width of the light diffusion incident angle region, but is a method intended to suppress the sticky feeling of a light diffusion film, there has been disclosed a method for producing a light diffusion film by performing light irradiation on a composition for light diffusion film in two times (for example, Patent Document 8).
That is, Patent Document 8 discloses a method for producing a light control plate (light diffusion film), characterized by irradiating a film-like body formed from a photopolymerizable composition formed on a sheet, with light from a particular direction, thereby curing the film-like body to obtain a cured film, subsequently laminating a transparent base material on the cured film so as to adhere closely, and then irradiating light.